1. Field of the Invention
This invention relates to a shaft bearing member having an oil groove formed in an inner circumferential face or sliding surface so as to circumferentially extend.
2. Description of the Related Art
Multiple cylinder engines for automobiles comprise a balance shaft provided in parallel with a crankshaft so as to be linked with the crankshaft in rotation so that vibration caused in the engine is reduced, for example. A plain bearing is usually used as a shaft bearing for supporting the balance shaft. Even if the balance shaft can reduce the vibration produced by the overall engine, the engine suffers a frictional loss due to the balance shaft with addition of a bearing for the balance shaft. Accordingly, provision of the bearing for the balance shaft becomes a disadvantageous condition. As a result, a reduction in the frictional loss in the bearing for the balance shaft has been desired.
Therefore, an object of the present invention is to provide a shaft bearing member which can reduce the frictional loss due to rotation of the shaft.
The present invention provides a shaft bearing member for supporting a shaft so that the shaft is rotatable, the shaft bearing member having an inner circumferential face serving as a sliding surface. The shaft bearing member comprises an oil groove formed in the inner circumferential face so as to circumferentially extend, and a recess formed in the inner circumferential face so as to extend from at least one of both widthwise sides of the oil groove toward an axial end of the inner circumferential face with respect to the shaft so that the recess is rendered shallower and shallower.
The lubrication oil supplied to the oil groove of the shaft bearing member flows through the oil groove onto the sliding surface with rotation of the shaft. An oil film pressure produced between the shaft and the sliding surface separates the shaft from the sliding surface. The inner circumferential face serving as the sliding surface has the recess formed in the inner circumferential face so as to extend from at least one of both widthwise sides of the oil groove toward an axial end of the inner circumferential face with respect to the shaft so that the recess is rendered shallower and shallower. Accordingly, the lubrication oil in the oil groove more easily tends to flow through the recess toward the axial end side of the sliding surface, thereby facilitating formation of an oil film. Consequently, the frictional loss resulting from rotation of the shaft can be reduced since a direct contact between the shaft and the sliding surface is avoided.
To achieve the same object, the invention also provides a shaft bearing member for supporting a shaft so that the shaft is rotatable, the shaft bearing member having an inner circumferential face serving as a sliding surface. The shaft bearing member comprises an oil groove formed in the inner circumferential face so as to circumferentially extend, and two recesses formed in the inner circumferential face so as to extend from both widthwise sides of the oil groove toward both axial ends of the inner circumferential face with respect to the shaft respectively so that the recesses are rendered shallower and shallower. Since the recesses are formed in both widthwise sides of the oil groove, formation of the oil film is further facilitated, whereupon the frictional loss resulting from rotation of the shaft can further be reduced.
In a first preferred form, the inner circumferential face includes two flat faces formed near the axial ends thereof respectively so as to be parallel with an axis of the shaft. Consequently, the shaft can be supported well since the oil film is desirably formed on the flat faces.
In a second preferred form, each flat face has an axially outer end formed with an escape portion which retreats radially outward so as to become lower than the flat face. When the shaft swings with an axial inclination, there is a possibility that the shaft may locally contact both axial ends of the shaft bearing member. In view of this local contact, when the escape portion is formed near the axially outer end of the inner circumferential face, an occurrence of the local contact between the shaft and sliding surface can be prevented.
In a third preferred form, the inner circumferential face includes a crowned portion near the axial end thereof. In this construction, too, the shaft can be supported well by the crowned portion and an occurrence of the local contact between the shaft and sliding surface can be prevented.
In a fourth preferred form, the shaft bearing member is formed into a generally semicylindrical shape, and the recesses are formed in a circumferentially central portion of the inner circumferential face thereof and excluded in portions thereof near circumferential ends of the inner circumferential face respectively, said portions being formed with flat faces parallel with the axis of the shaft respectively. In a case where two semicylindrical shaft bearing members are combined together into a cylindrical bearing shaft member, the lubrication oil disadvantageously tends to flow out of the circumferential ends when the recesses extend to the circumferential ends of the inner circumferential face respectively. However, since no recesses are formed in the portions located near both circumferential ends, the lubrication oil can be prevented from flowing out of the circumferential ends.
In a fifth preferred form, the inner circumferential face includes a plurality of narrow grooves formed therein so as to extend obliquely relative to a rotation direction of the shaft from the oil groove through the recesses toward the axial end sides respectively. The narrow grooves guide a lubrication oil from the oil groove toward the axial end sides with rotation of the shaft. The narrow grooves are shallower and narrower than the oil groove. The lubrication oil supplied to the oil groove more easily tends to flow through the narrow grooves into a gap between the shaft and the sliding surface with rotation of the shaft, whereby formation of an oil film is facilitated.